Aenta's former chief Medicare actuary was placed on administrative leave after filing a whistle-blower lawsuit alleging pharmacy benefits manager CVS Caremark overbilled Medicaid and Medicare for prescription drugs, according to The Columbus Dispatch.

Here are four things to know about the lawsuit.

1. Sarah Behnke, Aetna's former chief Medicare actuary, filed the pending whistle-blower suit after her internal investigation found CVS Caremark has been allegedly overbilling the federal government for prescriptions since 2007, according to the lawsuit. Ms. Behnke accused CVS Caremark of inappropriately billing the government $1 billion-plus in fraudulent charges.

2. Aetna placed Ms. Behnke on administrative leave after the whistle-blower suit was unsealed in federal court in early April. The unsealing comes as CVS Health, the parent company of CVS Caremark, is attempting to buy Aetna for $69 billion.

3. Ms. Behnke's lawyer told The Columbus Dispatch Aetna's decision to place its then-Medicare actuary on administrative leave was "retaliatory and inappropriate."

4. CVS Caremark rejected the allegations and said it will hand documents over to the court by June 1. The company said it was unaware who filed the lawsuit until after its parent put out an offer to Aetna. CVS Health spokesperson Michael DeAngelis told the publication, "We believe this complaint is without merit, and we intend to vigorously defend ourselves against these allegations." Aetna officials declined The Columbus Dispatch's request for comment.